In general, directional couplers comprise at least two hollow conductors for conducting electromagnetic waves. The hollow conductors are also called wave guides, hollow wave guides, rectangular wave guides, HF-wave guides, hollow-metallic wave guides, etc. Hereinafter, the term hollow conductor is used for such an item. The directional couplers are passive components which are used in the field of high frequency engineering for splitting, decoupling or coupling electromagnetic waves guided through at least one of the hollow conductors. Several directional couplers can be used to form a combiner which is a cascaded arrangement of directional couplers and, thus, a combiner is also called cascaded power combiner. Since the several directional couplers are combined in a cascaded manner, the combiner can be used to combine several electromagnetic waves, for instance.
Typically, the hollow conductors are brazed or welded together along two side walls of the hollow conductors facing each other. These side walls are perforated in order to provide a coupling portion for the electromagnetic waves enabling an interaction of the electromagnetic waves propagating through the hollow conductors. Ensuring the interaction, many holes and/or slits are provided in the coupling portion wherein the number of holes and/or slits increases dramatically when a coupling with low losses (good coupling) shall be achieved, for instance a 3 dB coupling.
In general, the size and the position of the holes and/or slits result from a complex function in order to ensure the good coupling. This complicates the manufacturing of the directional coupler significantly. The same applies for the manufacturing of a combiner comprising several directional couplers.
Further, the combiner needs a lot of space due to the many holes and/or slits of each directional coupler when 3 dB directional couplers are used.